Grounding... the serious thread.

[wood_e]

Now I'm not an EE but I want to figure out what needs better grounding in our cars. I'm not trying gain any performance just an understanding of the importance of having things grounded to the block rather than the battery.

Like that strap on the back of the intake... what is that connected to and should it be replaced? Should the alternator bolt (on the top) be grounded in a better manner?

 

[Rockledge]

I'd also be interested in hearing more about the SHO's grounds, I have a basic understanding like John, but I'm sure there is more I can learn. :corn:

 

[SHO Nick]

I'd also be interested in hearing more about the SHO's grounds, I have a basic understanding like John, but I'm sure there is more I can learn. :corn:

Yes..I wouldnt mind replacing a few easy to get to ground on the motor

 

[SHOZ123]

The more the better. Seeing as the sensors and PCM operate at 12 and 5vdc then good connections are paramount. The Fluke article I posted in the other thread explains it all and how to test.

Voltage is pressure. With low voltage systems it doesn't take much corrosion to cause problems. The DC circuits too are more reliant on grounding too because what goes out must come back, unlike AC.

 

[SASHO91]

I have a thread on it somewhere....
Its under installed engine grounding kit......
if that helps.....

 

[KC2SHO]

The DC circuits too are more reliant on grounding too because what goes out must come back, unlike AC.

What?

 

[Off Road SHO]

The reasons for the grounds is to clear out all of the transient voltages that are present in modern day engine compartments and to get multiple points of grounding.

There are lots of things in the engine compartment that generate a magnetic field, such as wires. Any time current is passed through a wire, a magnetic field is generated. Any other metallic device that is within that magnetic field, picks up some of that field in the form of electricity.

Not only does the original wire lose some of it's current that it was trying to transport to some device, but the interloper wire picks up some current that it doesn't need and defintely shouldn't have.

This is why sensitive DC circuits need to be shielded; to keep outside currents out and its own current in. Shielding does a great job at this, but over distance, the shield can be carrying so much current that the shield itself will cause its own magnetic shield and induce a transient current into the wires it's trying to shield, so the shield must be grounded also.

The more grounds the better. I think there are about 30 gound points on SHOs.

Also, the movement of air also cause static electricty to form and this must also be attracted back to ground so as to not cause an electrostatic discharge. This is just like your common garden variety "carpet shock". And where do we have a tremendous amount of dry (not laden with gasoline) air? In our fancy intake system.



Tom

 

[SHOZ123]

What?

DC electrons must return to the battery at the negative post.

AC electrons will go to any earth ground point.

This is why DC is inherently safer. If you have ever been shocked by AC you know this.

 

[rangerj]

It sounds like we all need to know the "ground" rules!

Sorry, I could'nt resist!

Oops, did it again. Shocking isn't it? And you all thought you were insulated from puns?

Seriously, this is good learning stuff. Thanks folks. rangerj

 

[SHOZ123]

On my '97 I run all the grounds to one point on the body. All ground wires are then tired to the battery ground through copper this way.

When I added the headlight wire harness there is a ground at each headlight. I connected both these grounds together then ran a #14 wire to the main body ground.

The main body ground is connected to the battery with #6 wire, the fender and the upper motor is connected with #8 and the engine block is grounded with #6 wire. The PCM and firewall are connected to the upper motor ground.

 

[KC2SHO]

See below

 

[KC2SHO]

DC electrons must return to the battery at the negative post.

True

AC electrons will go to any earth ground point.

Somewhat true if you are talking about power supplied from the electric company. “earth ground” would lead one to believe you mean a grounded system with a grounding rod driven into the soil. If that’s not what you meant then it’s redundant.

This is why DC is inherently safer. If you have ever been shocked by AC you know this

Not true. But I don’t run across 120 volts DC too often.


The "ground" on your car is only a relative ground to the circuit within your car. It just so happens that the automotive industry uses the negative side of the circuit as ground. Did you know some old cars had positive "ground" systems? Some people use the terms “negative” and “ground” synonymously. When you are talking about your automobile’s circuitry that’s fine but, ground does not mean negative and it certainly isn’t always the path of least resistance. If I put a battery next to your car and touch the positive to the body what will happen? How about if I hook the positive terminal of a battery to the ground rod outside my house? Nothing, it’s a different circuit. Therefore saying that current always flows to “ground” is an invalid statement.

Current always prefers to flow in the path of least resistance, regardless of whether it is AC or DC. Sometimes this can be the ground. It’s also true to say that current will flow to the point of greatest difference. In your house for example, a 120 volt outlet has a hot, a neutral and a ground. Back at the service however, the ground and neutral are tied to the same buss. Also at the service there are 2 “hot” wires. If you measure the voltage between either of the hot wires and ground/neutral you will read 120 volts. If you measure the voltage between the two hot wires you will measure 240 volts. Why? Because the 2 hot wires are 180 degrees out of phase. Between the peak of one sine wave and the low of the other is a span of 240 volts (120V+ and 120V-). Current would choose this path over the ground if given the opportunity. Again, not a path to ground.

Here’s an interesting read: http://www.pbs.org/tesla/ins/ins_acdc.html

Back to the topic at hand. All of your sensors should be grounded at a common point. The reason for this is that your car is made of steel. Steel is not a very good conductor and has a high loss when compared to good conductors like copper. Grounding sensitive measurement devices at the same point ensures that the reference voltage for all of the sensors will be the same. In doing so the reading getting back to the computer will be more accurate.

 

[SHOZ123]

Quote:
DC electrons must return to the battery at the negative post.

True

Glad we can agree on something....

 

[SHOZ123]

Quote:
DC electrons must return to the battery at the negative post.

True

Glad we can agree on something....

Quote:
AC electrons will go to any earth ground point.



Somewhat true if you are talking about power supplied from the electric company. “earth ground” would lead one to believe you mean a grounded system....

The correct NEC/ISO term is earth ground. In the 2005 NEC it is now required to bond the ground and neutral in the breaker box also.

This is why DC is inherently safer. If you have ever been shocked by AC you know this

Not true. But I don’t run across 120 volts DC too often.

I work with +600V DC every day but we are talking about a 12V DC car system. Soon to be 24V I hope.


I guess I should explain my thinking a bit.

When I am talking about the car's electrical system I am talking about the battery positive and negative post or something attached with wire to them.

If the ground or positive cable is insulated from the battery there is a 99.99% chance of no electron flow either through you or a wire or a piece of steel. If the battery has a acid film on the outside of the case this will conduct electricity. Most water is not a problem.

The reason to tie all the ground points together with copper is so that any resistance offered by the steel body will be negated by the copper tie in, but still let the steel act as a ground current carrier.